USING L*A*B* COLOR VALUES TO DETERMINE THE CHEMICAL, PHYSICAL, AND BIOLOGICAL COMPOSITION OF LAKE SEDIMENT CORE SAMPLES FROM SAN SALVADOR AND ELUTHERA, BAHAMAS

The effects of climate change and anthropogenic stress alter the hydrological and biogeochemical processes in lakes, affecting their floral and faunal communities. Lakes on carbonate platforms, such as in the Caribbean, include blue holes and hypersaline coastal lagoons. Blue holes are vertical karst dissolution structures that form in carbonate rock, with varying chemical and biological compositions. Sediment core samples were taken from several lakes on San Salavdor and Eluthera, Bahamas, in 2012 and 2013. One of the blue holes on Sal Salvador is located in the site of a historical plantation, and was more recently the location of a failed residential development; the other is relatively unimpacted. Basal dates range from ~6 to ~5 ky BP, reflecting sea level rise. High amounts of sand were incorporated into eolianite features at about 5000 BP, corresponding to slowing sea level rise about 4000 BP.

L*a*b* color values were extracted from exposure-corrected digital core images and compared to physical, biological, and chemical data from the cores. L*a*b* color values are designed to match human color vision and differentiate between color and light intensity. The L* value describes lightness-darkness, a* red-green, and b* blue-yellow. Data for color comparison include loss-on-ignition (LOI; carbonate and organic C content), mollusk shell abundance, scanning XRF (x-ray fluorescence elemental composition), and grain size. Due to cost and time constraints, samples for these analyses are typically taken only every 0.5 to 5 cm; however, where a strong correlation exists between the L*a*b* color values and the data, the equation of the regression line can be used to interpolate and predict the proxy values at all points on the core (50 micron pixels), allowing color to used as a high-resolution proxy for other measurements. This equation may differ between blue holes, so a relationship was developed for cores from two blue holes on San Salvador, and tested on cores from lakes on Eleuthera, a third blue hole (to test the same type of lake on a different island) and a hypersaline lagoon (to test a different type of lake).